1. Field of the Invention
The present invention relates to a manufacturing process for a semiconductor device by means of which improvements are achieved on accuracy and uniformity of a size of a transferred pattern in a pattern transfer step of the manufacturing process for a semiconductor device by suppressing optical distortion of an exposure apparatus, a photomask and a manufacturing apparatus for a semiconductor device.
2. Description of the Background Art
In an exposure apparatus used in manufacturing a semiconductor device, light radiated from a light source is transmitted through patterns on a photomask to be projected on a wafer surface to make an image. In FIGS. 28 and 29, shown are prior art photomasks formed by means of a prior art method. In FIG. 28, arranged are rectangular patterns 113a of the same shape having a side a in length in a uniform distribution on a photomask 103. Furthermore, in FIG. 29, formed is a single pattern 113b having a constant width L along a bending shape in photomask 103. A photoactive positive or negative photo resist is applied on a semiconductor wafer in advance. When apositive photoresist is employed, a part of the photoresist on which light through a photomask is irradiated is removed in a following developing step, while a non-irradiated part of the photoresist on which the light doesn""t irradiate remains in the following developing step. With such a process adopted, a pattern on the photomask is transferred on the wafer as a pattern of photo resist. By using the pattern of the photoresist, etching and impurity implantation are performed to manufacture a semiconductor device.
A photomask is manufactured such that as shown in FIG. 28, patterns of the same size are arranged in a repeated arrangement (periodical arrangement) and the same patterns are distributed in a uniform manner with respect to a size in each of regions all over the surface of the mask regardless of locality of a region to increase uniformity in terms of size of devices. Moreover, there is also included a step in which a non-repeated pattern (non-periodical pattern) as shown in FIG. 29 is transferred. The pattern with no repetition is also transferred by means of a transfer apparatus such that no variation in size occurs. Hence, each optical systems such as lenses of exposure apparatuses are designed and manufactured such that a pattern is transferred with uniformity.
Distortion in an optical system of an exposure apparatus is, however, difficult to be perfectly eliminated and in addition, characteristics of the distortion are different in each exposure apparatus. For this reason, a pattern on a photomask is not necessarily transferred in a faithful manner. As a result, a transferred resist pattern is affected by optical distortion specific to each exposure apparatus, resulting in a variation in performance of a semiconductor device.
In order to solve such a problem, a proposal has been made on a photomask to correct optical distortion in an exposure apparatus (see Japanese Patent Laying-Open No. 60-167328 and Japanese Patent Laying-Open No. 8-95229). By use of such a photomask corrected with respect to optical distortion, a variation in performance of a semiconductor device is alleviated. Correction methods for optical distortion disclosed in the above described publications are, however, to correct positional displacements of points on a photomask, wherein objects for the correction are a direction of a displacement and a distance thereof. Therefore, there has remained a problem in that the correction of optical distortion is complex and that no recognizable improvement can be achieved without the correction with very high accuracy. Since in a manufacturing process of a semiconductor device, a tremendous number of photomasks are employed, even only photomasks used in manufacturing steps which affect characteristics of the semiconductor device are difficult to be corrected in advance when depending on too complex a correction method. Hence, in company with progress in microfabrication of a semiconductor device, there has been built up a demand for a manufacturing process for a semiconductor device capable of obtaining an exposure-transferred pattern with high accuracy in a simple and convenient manner.
It is an object of the present invention to provide a manufacturing process for a semiconductor device capable of correcting optical distortion of an exposure apparatus in simple and convenient manner, a mask for use in the manufacturing process, and a manufacturing apparatus provided with the mask for a semiconductor device.
A manufacturing process for a semiconductor device of the present invention is a manufacturing process for a semiconductor device including a step of transferring a pattern on a photomask onto a semiconductor wafer by means of an exposure apparatus. The manufacturing process regards optical distortion of an exposure apparatus as a variation in reduction rate of a transferred pattern in each of regions of a photomask and includes: a first step of transferring a fundamental pattern formed on a reference photomask for measuring the optical distortion to measure a size of the transferred pattern in a corresponding one of regions; and a second step of, based on a result obtained in the first step, forming a corrected photomask having a pattern corrected in the corresponding one of regions with respect to the optical distortion.
According to such a constitution, an optical distortion can be obtained as a size of a pattern in each region on a photomask, or a rate of a size of a transferred pattern in a corresponding region and a size of a pattern on the photomask. The size and size rate can be obtained with ease, and furthermore, a corrected photomask can be fabricated based on the size or size rate in a simple and convenient manner. For this reason, a tremendous number of photomasks for use in manufacturing steps to affect characteristics of a semiconductor device can be replaced with respective corrected photomasks in a simple and convenient manner. Consequently, not only can a variation in a transferred pattern in each of exposure apparatuses can be restricted, but a dimensional variation in each of portions in a semiconductor device caused by optical distortion, which differs between exposure apparatuses, can be suppressed, such that sizes of portions in a semiconductor device formed through a different exposure apparatus can be all uniform. As a result, miniaturized semiconductor devices with high reliability can be provided with a high manufacturing yield. Note that optical distortion appears as a variation in a magnification rate or reduction rate in each region; therefore, the above described fundamental patterns are desirably provided across all regions of a reference photomask.
In the manufacturing process for a semiconductor device of the present invention, a fundamental pattern on the reference photomask is, for example, a plurality of unit patterns of the same shape arranged on the reference photomask.
By providing a reference photomask having unit patterns arranged thereon as described above, the area of a photomask is divided into regions including each unit pattern and a magnification rate or reduction rate can be obtained in each region. In a corrected photomask, a pattern size is corrected in each region based on a magnification rate or reduction rate for the region. This correction is performed such that a product of a magnification rate or reduction rate in each region and a pattern size in a corresponding region of a corrected photomask is the same as each other in any of all the regions regardless of particularity of a region. By use of the corrected photomask, when patterns of the same shape are intended to be disposed, for example, in a repeated arrangement (periodical arrangement) in a transferred pattern, the same patterns can be obtained in the respective regions as intended, in the transferred pattern.
In the manufacturing process of a semiconductor device of the present invention, a fundamental pattern on the reference photomask may be, for example, a non-periodical pattern with no periodicity formed on the reference photomask.
In manufacture of a semiconductor device, there are many cases where a single pattern with no periodicity is transferred and such a non-periodical pattern is necessary to be corrected with respect to a variation in size due to optical distortion. In a case of the non-periodical pattern as well, correction of a variation in size is effected by correcting a variation in reduction rate of each region similar to the case of a periodical pattern. As a result, a size accuracy in a pattern is improved and a variation in size between semiconductor devices processed by respective different exposure apparatuses can be restricted.
In the manufacturing process for a semiconductor device of the present invention, the first step desirably includes: for example, a step of obtaining a reduction rate which is a rate between a size of the transferred fundamental pattern and a size of the fundamental pattern on the reference photomask in each of regions of the reference photomask.
By obtaining a reduction rate in each of the regions, a corrected photomask can be manufactured with simplicity and convenience. When it is intended that the same patterns are provided in respective regions in a transferred pattern, patterns on a corrected photomask have only to be formed such that a size of each of the respected patterns on the corrected photomask is in inverse proportion to a reduction rate of a corresponding region. In the manufacturing process for a semiconductor device of the present invention, it is desirable that in the second step, for example, a size of a pattern in each of the regions of the corrected photomask is desirably formed such that a corrected reduction rate which is a rate between a size of a corrected, transferred pattern that is a transferred pattern of a pattern of the corrected photomask and a size of a pattern on the photomask prior to the correction in each of the regions is the same throughout all the regions regardless of each locality.
According to the above described constitution, optical distortion of an exposure apparatus is eliminated and a transferred pattern as intended can be obtained. For this reason, even when a transfer step is performed in a different exposure apparatus, photoresist patterns of the same size or the like are formed on a semiconductor substrate; and etching, impurity implantation and others can be performed based on the photoresist patterns of the same size. As a result, semiconductor devices with a high manufacturing yield, high reliability and high performance can be provided with simplicity and convenience.
In the manufacturing process for a semiconductor device, in the second step, for example, a size of a pattern in each of the regions of the corrected photomask is desirably formed such that a product of a pattern correction rate which is a rate between a size of a pattern in a region on the corrected photomask and a size of a pattern in a corresponding region of the photomask prior to the correction and a reduction rate in the region is the same regardless of which of all the regions the region belongs to.
The photomask prior to the correction is a photomask in a case where it is assumed that no optical distortion is present in an exposure apparatus and may be either existent or imaginary. By forming a pattern on a corrected photomask as described above, when the corrected photomask is used in the exposure apparatus, the optical distortion can be eliminated in terms of size. As a result, patterns which have been transferred in different ways in respective different exposure apparatuses can be transferred in a similar way as each other regardless of an exposure apparatus; therefore, high reliability semiconductor devices can be manufactured with a high manufacturing yield. Note that the above described pattern may be either a pattern set constituted of the same pattern repeatedly arranged in each of regions in a similar way or a pattern with no periodicity (non-periodical pattern) arranged across regions.
In the manufacturing process for a semiconductor device of the present invention, it is desirable that in the second step, for example, a pattern of a prescribed portion of the semiconductor device are arranged in each of the regions of the corrected photomask in a similar way, and a size of a pattern in each of the regions of the prescribed portion of the semiconductor device is determined such that a product of a size of a pattern of the prescribed portion of the semiconductor device in a region on the corrected photomask and a reduction rate in the region is the same all over the regions regardless of which of all the regions the region belongs to.
In a case where a pattern set is constituted of patterns of the same shape arranged in respective regions, a photomask prior to correction is not necessary to be referred to but a corrected photomask can be manufactured according to the above described constitution. By using the corrected photomask in the exposure apparatus, optical distortion can be eliminated in terms of size, thereby enabling manufacturing a high reliability semiconductor device with a high yield.
In the manufacturing method for a semiconductor device of the present invention, it is allowed that the second step includes a photomask manufacturing process and a pattern of the corrected photomask may be corrected in terms of size by adjusting at least one of a writing beam diameter and a writing dose with respect to a position of the corrected photomask in a resist writing step of the photomask manufacturing process.
In a case where a positive resist is used, a resist-lacking section occurs covering a large area if a writing beam diameter and a writing dose is large. That is, since an area of a resist-lacking section is in proportion to a writing beam diameter or a writing dose, a size of a pattern in each region can be adjusted by controlling such factors. The adjustment of a size in this case is not so large as to produce a change in shape of a pattern, but only at a subtle level of the order to be perceptible by an expertise, which is achieved by controlling at least one of a writing beam diameter or a writing dose as described above. Hence, by controlling the factors in a proper manner, an appropriate correction can be effected in a simple and convenient manner with good efficiency.
In the manufacturing process for a semiconductor device of the present invention, it is allowed that the second step includes a photomask manufacturing process and a pattern on the corrected photomask is corrected in terms of a size by adjusting a way of supply of a developer in a resist developing step of the photomask manufacturing process.
The adjustment can also be performed in a resist developing step. A developing reaction is accelerated at a writing site supplied with a fresh, unused developer and thereby, resist removal progresses ahead of the other sites to a larger extent there. For this reason, by adjusting a position and a direction of a nozzle; a residence time at each site of a nozzle, if movable; in addition, a discharge amount of a developer; and others, formation of a corrected pattern with a desired pattern size distribution is effected. Since the optical distortion, in many cases, differs at a degree thereof in each of regions partitioned concentrically, formation of a pattern in each of the regions may be sufficiently controlled, in many cases, if the photomask is separated into central and peripheral regions and an intermediate region therebetween. Note that correction of an area of a resist-lacking section can also be effected on an area of a writing site of the same magnitude.
In the manufacturing process of a semiconductor device of the present invention, it is also allowed that the second step includes a photomask manufacturing process and a pattern on the corrected photomask is corrected in terms of size by adjusting a way of supply of an etching liquid in a wet etching step for a Cr film in the photomask manufacturing process.
The way of supply of a developer applies to a way of supply of the etching liquid in the wet etching of a Cr film without any change therein. Hence, a size of a Cr film-lacking section can be corrected even when an area of a resist-lacking section is the same.
In the manufacturing process of a semiconductor device of the present invention, it is also allowed that the second step includes a photomask manufacturing process and a pattern of the corrected photomask is corrected in terms of size by adjusting a strength of a magnetic field in a dry etching step for a Cr film of the photomask manufacturing process.
By adjusting a strength of a magnetic field, a flow of a plasma gas, which is constituted of an etching gas, can be controlled. As a result, a desired, corrected photomask can be obtained by adjusting an etching rate in each of central and peripheral regions and an intermediate region therebetween.
In the manufacturing process for a semiconductor device of the present invention, it is desirable that the magnetic field in a dry etching step for the Cr film is a rotating magnetic field formed such that a combination of two orthogonal magnetic fields are applied in synchronism with each other in parallel to a surface of the corrected photomask and adjustment of a strength of the magnetic field is effected by controlling the two magnetic fields independently of each other.
By adjusting the two magnetic fields independently of each other, the center of the rotating magnetic field can be migrated along a surface of the photomask. Hence, when optical distortion occurs in one side portion of the photomask or in the like case, the above described constitution is preferable in correcting such a kind of optical distortion. Moreover, this can applies to cancellation of optical distortion whose degree changes along a concentric circle.
In the manufacturing process of a semiconductor device of the present invention, it is also allowed that the second step includes a photomask manufacturing process and a pattern on the corrected photomask is corrected in terms of size by combining factors for a change in size of a pattern in at least two steps among a resist writing step, a resist developing step and a Cr film etching step of the photomask manufacturing process.
As described above, a size of a pattern in each of regions can increase or decease with a larger adjustment width by combining at least two steps. Hence, as high degree an optical distortion as not to be adjustable in a single step of an exposure apparatus can be adjusted with simplicity and convenience.
A photomask of the present invention is a photomask having a pattern thereon, employed in transfer of the pattern onto a semiconductor wafer by means of an exposure apparatus. Correction of a size of a pattern on the photomask is performed such that correction is effected on a variation in reduction rate of a transferred pattern in each of regions caused by optical distortion of the exposure apparatus.
This photomask is a corrected one described above and the photomask can be fabricated with simplicity and convenience. Since optical distortion on a pattern on the photomask is corrected in terms of size, a transferred pattern with an as-intended size can be obtained in each of regions thereof.
In the photomask of the present invention, a reduction rate can be regarded to be one as measured in each of the regions of a transferred pattern from a fundamental pattern formed on a reference photomask exclusively used in measurement of optical distortion of an exposure apparatus.
Since optical distortion is measured as a size of each of regions, the optical distortion can be evaluated with much of simplicity and convenience and a method for reflecting the measured optical distortion on fabrication of a corrected photomask is also very simple and convenient. Therefore, a tremendous number of photomasks required in a manufacturing process for a semiconductor device can be replaced only with a necessary number of corrected ones in a simple and convenient manner. As a result, for example, a semiconductor device having a memory capacity larger than a currently available one by one rank can be manufactured using currently existing facilities with none of an additional large investment thereon.
A manufacturing apparatus for a semiconductor device provided with a photomask of the present invention is a manufacturing apparatus for a semiconductor apparatus to transfer a pattern arranged on a photomask onto a semiconductor wafer to perform exposure. In the manufacturing apparatus for a semiconductor device, the photomask is disposed between a light source for exposure and the semiconductor wafer.
By employing the above described manufacturing apparatus for a semiconductor device, a high reliability semiconductor device can be provided with a high yield.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.